Weed Community Assembly Research Articles

Fertility and tillage intensity affect weed community diversity and functional structure in long-term organic systems.

Knowledge of how agricultural management interacts with weed seed banks and emergent weed communities is crucial for proactive weed management. Though studies have detailed how differences in disturbance and nutrient applications between organic and conventional herbicide-based systems affect weed communities, few have focused on these same factors in contrasting organic systems. This study assessed the seed banks and emergent weed communities from the most recent crop rotation cycle (2017-2022) of a long-term experiment, which compared four organic grain and forage cropping systems differing in nutrient inputs and soil disturbance. The high fertility (HF) system received high-rate nutrient applications, low fertility (LF) received low-rate applications, enhanced weed management (EWM) focused on weed control through frequent soil disturbance, and reduced tillage (RT) prioritized soil health with less intense or frequent soil disturbance. Soil samples for greenhouse germination assays were collected at the beginning (2017) and end (2022) of the rotation to explore how these four systems influenced seed bank dynamics over time. Weed community biomass was also sampled in each crop during this time. Treatment effects on weed abundance, taxonomic diversity, and community-weighted means and functional dispersion of weed traits were analyzed with generalized mixed-effect models. The RT system had the highest weed seed bank taxonomic diversity, and EWM had the lowest. RT and LF had higher functional dispersion of traits than HF in the seed bank. Weed seed bank communities in HF and RT were characterized by short, small-seeded, and early germinating weed species. However, seed banks were also labile: Differences between systems in seed density and all other mean trait values were dependent on the crop, which preceded seed bank sampling. Likewise, differences among emergent weed communities in the four systems depended on an interaction between crop species and their planting year. Results suggest that resource availability and intensity of disturbance act as weed community assembly filters in organic cropping systems. Organic growers seeking to design systems that balance weed management and production goals can use relatively low soil disturbance and nutrient application to increase weed community taxonomic or functional diversity without necessarily increasing weed biomass or seed bank density.

Characterisation of Czech arable weed communities according to management and production area considering the prevalence of herbicide‐resistant species

AbstractHerbicide resistance is a widespread issue that impacts management of conventional farms, but also has ramifications for the weed community assembly; it is therefore important to see how these species factor into the weed community assembly of farms throughout the countryside. This research analysed species richness and community diversity in 98 field relevés from 48 organic and 50 conventional farms evenly distributed between two major production regions of the Czech Republic and then evaluated the incidence of species which have been reported resistant in the Czech Republic and its neighbouring countries. Farms were selected independently of any acknowledged resistant species. Out of 164 species found in this survey, only eight species have had herbicide‐resistant biotypes reported in the Czech Republic, while a total of 19 species had herbicide‐resistant biotypes reported in neighbouring countries. Species with recorded resistance to PSII inhibitors in the Czech Republic tended to be found together and were mostly associated with the beet production region, characterised by low altitude: Amaranthus retroflexus, Chenopodium album, Echinochloa crus‐galli and Solanum nigrum. Species with reported resistance to ALS and ACCase‐inhibiting herbicides were not clearly associated with a particular region or farming type. Of the species which have had reported herbicide resistance in the neighbouring countries, several were found in conventional fields within the growing season and we recommend immediate screening for herbicide resistance in these species and more diligent action in management according to anti‐resistance strategies: Bromus sterilis resistant to ACCase‐inhibiting herbicides, A. retroflexus resistant to ALS‐inhibiting herbicides or Avena fatua resistant to ACCase and ALS‐inhibiting herbicides. This work is unique in that it is evaluating weed species diversity in organic and conventional farms and using the context to frame the prevalence of high‐risk herbicide‐resistant species; thereby putting the potential incidence of herbicide resistance into perspective at the landscape level.

Weed Communities in Winter Wheat: Responses to Cropping Systems under Different Climatic Conditions

Understanding the impact of biological and environmental stressors on cropping systems is essential to secure the long-term sustainability of agricultural production in the face of unprecedented climatic conditions. This study evaluated the effect of increased soil temperature and reduced moisture across three contrasting cropping systems: a no-till chemically managed system, a tilled organic system, and an organic system that used grazing to reduce tillage intensity. Results showed that while cropping system characteristics represent a major driver in structuring weed communities, the short-term impact of changes in temperature and moisture conditions appear to be more subtle. Weed community responses to temperature and moisture manipulations differed across variables: while biomass, species richness, and Simpson’s diversity estimates were not affected by temperature and moisture conditions, we observed a minor but significant shift in weed community composition. Higher weed biomass was recorded in the grazed/reduced-till organic system compared with the tilled-organic and no-till chemically managed systems. Weed communities in the two organic systems were more diverse than in the no-till conventional system, but an increased abundance in perennial species such as Cirsium arvense and Taraxacum officinale in the grazed/reduced-till organic system could hinder the adoption of integrated crop-livestock production tactics. Species composition of the no-till conventional weed communities showed low species richness and diversity, and was encompassed in the grazed/reduced-till organic communities. The weed communities of the no-till conventional and grazed/reduced-till organic systems were distinct from the tilled organic community, underscoring the effect that tillage has on the assembly of weed communities. Results highlight the importance of understanding the ecological mechanisms structuring weed communities, and integrating multiple tactics to reduce off-farm inputs while managing weeds.

Cereal rye mulch biomass and crop density affect weed suppression and community assembly in no‐till planted soybean

AbstractThe use of multiple ecological weed management tactics may be an effective solution to weed management challenges associated with reducing tillage. An experiment was conducted to assess how soybean Glycine max (L.) Merr. density and cereal rye Secale cereale L. mulch biomass affected weed suppression and community assembly in no‐till production. Soybean was planted at five rates from 0 to 74 seeds m−2, and five cereal rye mulch levels were established from 0 to 2 times the ambient cereal rye biomass within each site–year. We assessed the effects of soybean density and cereal rye mulch biomass on weed suppression, weed community composition, and the functional structure of weed life cycle, emergence timing, seed weight, height, and specific leaf area traits. Weed suppression was influenced by a synergistic interaction between soybean density and cereal rye biomass. The functional dispersion (FDis) of all weed traits, when combined, was reduced by increased soybean density and mulch biomass, suggesting that high treatment intensities induced trait convergence. However, soybean density and cereal rye biomass had differing effects on the FDis and composition of individual traits, suggesting that these management practices represent unique filters during weed community assembly. Mulch biomass had a larger effect on annual weed suppression and weed community composition than soybean density. Farmers who utilize high biomass cover crop mulch for weed management may experience shifts in weed community composition toward an increased proportion of perennials and weeds with later emergence, heavier seeds, and shorter stature. Increasing soybean density may reduce perennial weed biomass, making it a valuable complement to high cereal rye mulch biomass. As such, weed management in no‐till soybean is enhanced by combining multiple practices, which can enable synergistic weed suppression and the management of diverse weed functional groups.

Populations of arable weed species show intra-specific variability in germination base temperature but not in early growth rate.

Key plant traits affecting growth performance can differ among and within species, influencing competitive plant community dynamics. We determined the intra-specific variability of germination base temperature among 13 arable weed species and the seedlings' early post-emergence relative growth rate among 21 species in climate chamber and green house experiments. Intra-specific variability was quantified with two seed populations (originating from contrasting climate in Germany & France) for the germination base temperature of 6 species and for the early growth rate of 16 species. Inter-specific variability for both traits was always higher than intra-specific variability. Within a given species, we found that germination base temperatures were higher in seeds stemming from colder climate populations. Seedling relative growth rates did not differ between seed populations. Models simulating weed growth should reflect these differences in germination traits among populations, especially when they are used for weed community assembly studies in a local to regional extent.

Long‐term farming systems and last crop sown shape the species and functional composition of the arable weed seed bank

AbstractQuestions: The assembly of arable weed communities is the result of local filtering by agricultural management and crop competition. Therefore, soil seed banks can reflect the effects of long‐term cumulative field management and crop sequences on weed communities. Moreover, soil seed banks provide strong estimates of future weed problems but also of potential arable plant diversity and associated ecological functions. For this, we evaluated the effects of different long‐term farming systems under the same crop rotation sequence on the abundance, diversity and community assembly of weed seed bank, as well as on the functional diversity and composition.Location: DOK (biodynamic [D], bioorganic [O], conventional [K]) long‐term trial, Therwil, Switzerland.Methods: The effects of long‐term contrasted farming systems (i.e., biodynamic, organic, conventional, mineral and unfertilised systems) and last crop sown (i.e., wheat and maize) were evaluated on different indicators of species and functional diversity and composition of the weed soil seed bank.Results: The results showed significant influences of 40 years of contrasted farming systems on the diversity and composition of the seed bank, with higher diversities being found in unfertilised and organic farming systems, but also higher abundances than those found under conventional systems. Organic farming also allowed higher functional richness, dispersion and redundancy. Different farming systems triggered shifts in species and functional assemblies.Conclusions: The results highlight the importance of organic management for the maintenance of a diverse arable plant community and its functions. However, such results emphasise the need for appropriate yearly management to reduce the abundance of settled weediness and prevent affecting crop production. The farm management filtered community composition based on functional traits. Although the soil seed bank buffers the long‐term farming and crop sequence, the last crop sown and, thus, the yearly management were important determinants of seed bank composition.

Increased crop diversity reduces the functional space available for weeds

SummaryThere is a drive to improve the sustainability of agricultural systems including the biodiversity component. Cultivar mixtures offer yield benefits from the same land area, but the mechanisms behind this overyielding have not been completely worked out. One potential mechanism is improved competition with weeds. We use an experimental approach of varying barley (Hordeum vulgare L.) genotypic and phenotypic diversity to test the hypothesis that increases in diversity have an impact on weed growth strategies and community assembly, or if responses are driven by barley performance. There was no effect of increasing barley mixture diversity on weed traits, either in terms of species means or the community‐weighted mean. However, Functional Richness of the weed community decreased with increasing barley mixture diversity mainly as a result of reduced specific leaf area Functional Richness. This pattern was driven by a reduction in species richness of the weed community rather than by reduced variation within species. Whilst barley phenotype had different impacts on weed traits, there were no specific mixtures of phenotypes or genotypes that had consistent effects on community assembly or weed species responses. The competitive exclusion of weed species could have agronomic and environmental benefits, through better targeting or less frequent use of herbicides. Growing crop mixtures is one of many strategies available to improve agricultural sustainability and resilience, and one that has clear benefits.

Weed Communities in Semiarid Rainfed Croplands of Central Argentina: Comparison between Corn (Zea mays) and Soybean (Glycine max) Crops

AbstractThe semiarid Espinal in central Argentina, being recently transformed from natural semiarid grasslands into agriculture, represents an interesting scenario to understand the early stages of weed community assembly and its relationship with crop identity and management. Our aim was to characterize the weed communities in corn (Zea maysL.) and soybean [Glycine max(L.) Merr.], the main crops of the Espinal region, under the dominant rainfed conditions. Weed surveys were carried out in 53 fields, and farmers were interviewed to collect information about crop management. Floristic composition was compared within and between crops by calculating the additive partition of the abundance-based Bray-Curtis dissimilarity. We compared the frequency and mean cover of functional groups between crops through generalized linear models. Finally, canonical correspondence analysis was carried out to analyze the associations between floristic composition and agronomic variables. Mean alpha and gamma diversity was greater in corn (10.0 and 80 species, respectively) than in soybean (7.6 and 46 species, respectively). Furthermore, species composition of weed communities was more similar among soybean fields than among either cornfields or fields of both crops. Hence, floristic differences between crops are potentially the result of different microenvironmental heterogeneity above- and belowground, with corn likely to be more permissive to weed establishment compared with soybean. The higher frequency of annual, dicotyledonous, and native species, and the high proportion of rare species, mostly native, suggest a strong legacy of the original vegetation that thrived in these recently cultivated systems. The functional composition was also affected by agronomic management, with sulfur, nitrogen, and grass herbicide application being the most important factors related to the floristic composition of weed communities. This early description can be used as a starting point for studies concerning trajectories, mechanisms, and processes of weed communities related to environment and management.

Patch dynamics and temporal dispersal partly shape annual plant communities in ephemeral habitat patches

Most organisms in ephemeral habitat patches have resting stages which form a local species pool in response to temporal variations in the patch's availability and suitability. Temporal dispersal from the local species pool may, therefore, be an important process shaping the community assembly, particularly soon after patch creation, and possibly interacting with environmental filtering. As the temporal variation of the environmental conditions has a major effect on the composition of the local species pool, we investigated how well contemporary conditions (both patch availability and patch suitability) and temporal dispersal (approximated by environmental temporal variation and temporal distance) explain the changes in community composition in a given locality through successive ephemeral habitat cycles. We used arable weeds in annual crops as models. We calculated temporal weed community dissimilarity indices between weed communities surveyed in cropping seasons at intervals of two to eight years within a given field. The weeds were surveyed twice each cropping season to account for any changes in the relative contributions of temporal dispersal and contemporary conditions during the season. Patch availability explained most of the temporal weed dissimilarity, suggesting that patch dynamics have the greatest effect on weed community assembly. Temporal distance and temporal variation of the environmental conditions had more effect at the start of the cropping season than later, while patch suitability had more effect in the middle of the season. These results suggest that temporal dispersal drives the weed community assembly when ephemeral habitat patches are created. These assemblies are further shaped by environmental filtering. This is consistent with a temporal source sink dynamic mechanism where the seed bank acts as the main weed source. However, a large part of temporal weed dissimilarity remains unexplained, suggesting that other ecological processes such as spatial dispersal and founder effect may also shape the weed community.

How do weeds differ in their response to the timing of tillage? A study of 61 species across the northeastern United States

AbstractPrevious research has demonstrated that the season in which soil is tilled (spring versus fall) can strongly influence weed community assembly and subsequent species composition and abundance in annual cropping systems. Despite this understanding, it is unknown whether finer‐scale, within‐season variation in the timing of tillage has similar impacts on weed community assembly. We conducted an experiment on four research farms across the northeastern USA to test the effects of tillage timing on weed emergence periodicity. Soil was tilled at 12 different times that were 2 weeks apart from 29 April to 30 September (the entire growing season) and the composition and abundance of the weed seedlings that emerged was measured 6 weeks later. Weed species clustered into three tillage timing groups at the two New York locations and clustered into five tillage timing groups at the New Hampshire and Maine locations. Individual species associated with each window of tillage time varied by location. No single trait or combination of traits were consistently associated with species‐by‐tillage time groupings across locations; however, within each location several traits were associated with particular groups of species, including: (a) seed length, (b) seed weight, (c) cotyledon type, (d) life span, (e) ploidy level and (f) photosynthetic pathway. These results suggest that fine‐scale variation in the timing of tillage can lead to predictable changes in the species composition and trait distribution of weed communities in annually tilled agroecosystems.

Disentangling the Effects of Tillage Timing and Weather on Weed Community Assembly

The effect of tillage timing on weed community assembly was assessed at four locations in the Northeastern United States by tilling the soil every two weeks from April to September and quantifying the emerged weed community six weeks after each tillage event. Variance partitioning analysis was used to test the relative importance of tillage timing and weather on weed community assembly (106 weed species). At a regional scale, site (75.5% of the explained inertia)—and to a lesser extent, timing—of tillage (18.3%), along with weather (18.1%), shaped weed communities. At a local scale, the timing of tillage explained approximately 50% of the weed community variability. The effect of tillage timing, after partitioning out the effect of weather variables, remained significant at all locations. Weather conditions, mainly growing degree days, but also precipitation occurring before tillage, were important factors and could improve our ability to predict the impact of tillage timing on weed community assemblages. Our findings illustrate the role of disturbance timing on weed communities, and can be used to improve the timing of weed control practices and to maximize their efficacy.

Which Traits Allow Weed Species to Persist in Grass Margin Strips?

Sown-grass margin strips, historically established to limit pesticide drift and soil erosion, are now also promoted for enhancing floral diversity and associated ecosystem services. To better understand weed community assembly in grass margin strips, we performed floral surveys in 75 sown-grass margin strips in two regions in France and characterized each species using information from trait databases. We hypothesized that traits of dominant species would differ between newly sown-grass margin strips and older strips. Weed species were separated into functional groups based on their traits using multiple correspondence analysis and hierarchical ascendant classification. Functional group trajectories were investigated in sown-grass margin strips that differed in age using a space-for-time substitution approach. We found that geophyte, competitor, and monocotyledon species were more frequent and abundant in grass margin strips than therophyte, ruderal, and dicotyledon species. Results also showed that floral diversity was greatest in grass margin strips of intermediate age. Our findings have implications for optimizing diversity and ecosystem services on land enrolled in conservation programs and suggest that mowing later in the season and periodic soil disturbance can increase floral diversity. The analytical framework that we introduced in this research can also be used to explore weed community assembly in other systems.

Trophic Relationships between the Parasitic Plant Species Phelipanche ramosa (L.) and Different Hosts Depending on Host Phenological Stage and Host Growth Rate.

Phelipanche ramosa (L.) Pomel (branched broomrape) is a holoparasitic plant that reproduces on crops and also on weeds, which contributes to increase the parasite seed bank in fields. This parasite extracts all its nutrients at the host’s expense so that host–parasite trophic relationships are crucial to determine host and parasite growth. This study quantified the intensity with which P. ramosa draws assimilates from its host and analyzed whether it varied with host species, host phenological stage and host growth rate. A greenhouse experiment was conducted on three host species: the crop species Brassica napus (L.) (oilseed rape) and two weed species, Capsella bursa-pastoris (L.) Medik. and Geranium dissectum (L.). Plants were grown with or without P. ramosa and under three light levels to modulate host growth rate. The proportion of host biomass loss due to parasitism by P. ramosa differed between host species (at host fructification, biomass loss ranged from 34 to 84%). B. napus and C. bursa-pastoris displayed a similar response to P. ramosa, probably because they belong to the same botanical family. The sensitivity to P. ramosa in each host species could be related to the precocity of P. ramosa development on them. Host compartments could be ranked as a function of their sensitivity to parasitism, with the reproductive compartment being the most severely affected, followed by stems and roots. The proportion of biomass allocated to leaves was not reduced by parasitism. The proportion of pathosystem biomass allocated to the parasite depended on host species. It generally increased with host stage progression but was constant across light induced-host growth rate, showing that P. ramosa adapts its growth to host biomass production. The rank order of host species in terms of sink strength differed from that in terms of host sensitivity. Finally, for B. napus, the biomass of individual parasite shoots decreased with increasing their number per host plant, regardless of host growth rate. Results will be incorporated into a mechanistic model in order to analyze the effect of parasitic plant species on weed community assembly and to design new cropping systems for controlling P. ramosa.

Changes in functional diversity and intraspecific trait variability of weeds in response to crop sequences and climate

SummaryHow weed communities assemble represents one the key issues of weed science. For a decade, functional approaches have been applied to investigate the processes that govern weed community assembly. In most previous studies, trait values have been generally averaged over multiple populations and habitats. Consequently, conspecifics display similar trait values while neglecting the considerable influence of intraspecific variability to detect changes in functional diversity in response to environmental drivers. However, this influence has been shown to be critical, especially, at local scales. Here, we studied changes in weed functional diversity at the field scale in four crop sequences. We focused on intra‐ and interspecific variability of four key functional traits involved in response to resource acquisition processes, the latter being modified by climate, management and competition. The relative influence of intra‐ and interspecific variability among the crop sequence types was highlighted using a diversity partitioning approach. It provides evidence for substantial amount of intraspecific variability in the weed community and underlines its essential role in response to fine‐scale environmental drivers. In addition, we investigated the response of the three most abundant species to competition with the crop, the growing season and the crop sequence type. We highlighted that these species showed a wide range of combinations of trait values, suggesting the co‐existence of several successful strategies. Based on these results, we emphasise that neglecting intraspecific variability can lead to substantial underestimations of the functional weed response to management and crop‐weed competition at the field scale.

Impacts of cropping system and management practices on the assembly of weed communities

SummaryUnderstanding how weed communities assemble as a function of biotic and abiotic filters and transform through time has important implications for the sustainable management of agronomic systems. In a three‐year study, we evaluated weed community responses to lucerne (Medicago sativa, perennial) vs. continuous spring wheat (Triticum aestivum, annual, CSW) and weed management practices where weeds in the CSW system were managed with three contrasting approaches (herbicide, tillage or sheep grazing). Our results indicated no differences in weed diversity between the perennial and annual crops or across the different management practices in CSW. However, there were differences in weed community composition. Lucerne, with the exception of the establishing year, impeded the growth and reproduction of several annual weeds, including Amaranthus retroflexus, Thlaspi arvense, Lamium amplexicaule and Chenopodium album, but favoured perennial broad‐leaved weeds such as Taraxacum officinale and Cirsium arvense. The replacement of herbicide treatments in pre‐plant and post‐harvest in CSW with soil tillage or sheep grazing selected for different weed communities beyond the second year of establishment. The weed species driving the differences in CSW systems were Androsace occidentalis, more common in CSW managed chemically; Asperugo procumbens, more common in CSW managed with tillage; and T. officinale and Lactuca serriola, more common in CSW managed with sheep grazing. Understanding how cropping systems modify weed communities is a necessary step to shift from reactive weed control programmes to predictive management strategies.

Cover-Crop Species as Distinct Biotic Filters in Weed Community Assembly

Cover crops represent a potentially important biological filter during weed community assembly in agroecosystems. This filtering could be considered directional if different cover-crop species result in weed communities with predictably different species composition. We examined the following four questions related to the potential filtering effects of cover crops in a field experiment involving five cover crops grown in monoculture and mixture: (1) Do cover crops differ in their effect on weed community composition? (2) Is competition more intense between cover crops and weeds that are in the same family or functional group? (3) Is competition more intense across weed functional types in a cover-crop mixture compared with cover crops grown in monocultures? (4) Within a cover-crop mixture, is a higher seeding rate associated with more effective biotic filtering of the weed community? We found some evidence that cover crops differentially filtered weed communities and that at least some of these filtering effects were due to differential biomass production across cover-crop species. Monocultures of buckwheat and sorghum–sudangrass reduced the number of weed species relative to the no-cover-crop control by an average of 36 and 59% (buckwheat) and 25 and 40% (sorghum–sudangrass) in 2011 and 2012, respectively. We found little evidence that competition intensity was dependent upon the family or functional classification of the cover crop or weeds, or that cover-crop mixtures were stronger assembly filters than the most effective monocultures. Although our results do not suggest that annual cover crops exert strong directional filtering during weed community assembly, our methodological framework for detecting such effects could be applied to similar future studies that incorporate a greater number of cover-crop species and are conducted under a greater range of cover-cropping conditions.

Stochastic processes and crop types shape weed community assembly in arable fields

AbstractAimsIn agro‐ecosystems, crop types, i.e., the crop species and its associated agricultural practices, have been shown to influence the taxonomic as well as functional composition of weed communities. However, the processes underlying weed community assembly within a crop type are poorly understood, especially regarding the contributions of local factors and stochastic processes. In this study, we investigate the effects of the crop type in shaping local weed communities.LocationLTER Zone Atelier Plaine et Val de Sèvre, an intensive cereal system in western France.MethodsWe selected 105 fields of five crop types and investigated the functional structure of weed communities for those traits that define the Leaf–Height–Seed (L‐H‐S) strategy as well as phenological traits. We compared the observed trait distribution to trait distributions expected under random assembly. The trait distributions were described by the range, the community‐weighted mean and the dispersion of each trait, and simulated communities were generated with a null model approach that randomizes the ‘species × traits’ matrix to maintain equiprobable the occurrence of each trait combination. The relationship between trait values and species abundance within each community was investigated using Kendall rank correlation tests.ResultsOur results showed that, in ca. 90% of the fields, the functional diversity of weed communities did not differ from what would be expected under random assembly. Departures from random expectations essentially resulted from shifts in weighted mean values for phenological traits. Weed communities of sunflower, maize and spring pea had later onsets of emergence and flowering than randomly expected. Communities of winter wheat had smaller species and earlier onset of flowering, and communities from oilseed rape had a larger duration of the emergence period and earlier onset of flowering. In addition, we found a positive significant relationship between species abundance and trait values for phenology for spring pea, sunflower and maize, suggesting that species with a later onset of emergence and flowering period have higher performance in these weed communities.ConclusionsAt landscape scale, weed communities generally showed patterns of functional diversity in accordance with those expected under random community assembly, except for phenological traits in spring and summer crops, where patterns were rather consistent with environmental filtering.

Weed community composition after 43 years of long-term fertilization in tropical rice–rice system

Biodiversity is central to the study of biology and research on the effects of human activities on biodiversity is becoming increasingly important as extinction levels increase. Many factors are increasing extinction levels, and continuous nitrogen application may be one of the reason driving terrestrial extinctions. Understanding the response of arable weed community assembly to fertilization is important for designing better weed management strategies in tropical rice–rice systems and also for changes in weed biodiversity. The cumulative effects of various fertilization treatments on weed species composition and diversity along with rice growth and yield were investigated in a long-term fertilizer experiment established 43 years ago in CRRI, Cuttack, India. A total of 20 weed species were observed in the study, out of which 6 species (i.e., Cyperus difformis, Cyperus tenuspica, Fimbristylis miliacea, Echinochloa colona, Oldenlandia corymbosa, Lindernia anagallis) occurred in all treatments and remaining species occurred only in some of the treatments. Sedges were dominant in all the treatments followed by broad-leaves and grasses, high relative density of weeds was observed in control and FYM treated plots, whereas, low weed density was observed in N, NPK and NPK+FYM treatments. The indices of species diversity (species richness, Shannon–Wiener, Pielou and Simpson indices) showed linear relationships with rice yield. The balanced fertilization was more efficient at inhibiting the potential growth of weeds because of the increased growth of rice leading to competition for nutrients. Principal component analysis showed that changes in the weed community composition were due to application of P and FYM. Balance fertilization showed a positive effect on rice yield and negatively affect weeds density, although the effect is negative but balance fertilization is not resulted in species elimination or hampered biodiversity.

The ecophysiological determinants of nitrophily in annual weed species

SummaryPlant nitrophily plays a key role in weed community assembly. To date, the determinants of the success of nitrophilic weeds and of the decline of oligotrophic weeds in intensive cropping systems are not fully understood. This study investigated which ecophysiological traits related to carbon and N nutrition explain plant nitrophily in field annual species. Twelve species (consisting of monocotyledonous and dicotyledonous species, as well as crops and weeds) covering the oligotrophic‐nitrophilic continuum were grown in a glasshouse experiment at two contrasted conditions of soil‐nitrogen supply. From measured plant growth variables, ecophysiological traits were calculated to account for plant nutritional strategies. Globally, whatever the soil‐nitrogen supply, increased nitrophily was associated with a decreased allocation of carbon to root vs. shoot. At high soil‐nitrogen only, increased nitrophily was also generally associated with an increased nitrogen uptake activity per unit of root biomass, pointing to a trade‐off between oligotrophic species with a preferential carbon investment in root structure and nitrophilic species with a preferential carbon investment in root activity. Beyond these global trends explaining nitrophily, results also show that different strategies are possible for plant species to be considered as nitrophilic. This study provides evidence on why adjusting N fertilisation in quantity, in space (with nitrogen fertiliser placement on the row) or in time can be useful strategies to manage the most nitrophilic weeds, which are also the most problematic in intensive cropping systems.

Refining rare weed trait syndromes along arable intensification gradients.

QuestionHow does the conservation (rarity) value of arable weed communities differ along intensification gradients? Which functional traits best distinguish the weed communities of more and less extensively managed fields? Can the same traits predict the rarity of individual weed species?LocationHungary.MethodsUsing relevé data from 60 cereal and 70 stubble fields, together with weed trait data, we characterized community responses to arable intensification using functional trait analyses based on trait‐convergence and trait‐divergence assembly patterns. We also examined how well the broad‐scale rarity status of species predicts their occurrence along intensification gradients, and how it maps onto our functional classifications describing intensification responses.ResultsThe response of weeds to intensification in cereal fields was best described by a functional classification based on species' flowering duration, maximum height and seed weight: weeds of extensively managed fields have short flowering seasons (2–5 mo) and particularly large or small seeds. The highest proportions of rare species also happen to be found in these groups. The rarest weeds among these species tend to be late‐winter and early‐summer annuals, while the rare species of stubble fields tend to be broad‐leaved with low nitrogen requirements, small seeds and short height. Stubble fields showed a decline in weed cover with increasing application of fertilizer and distance from the field edge, but we could detect no strong associations of management factors with trait composition, perhaps because the intensification gradient across these fields was shorter.ConclusionsMany rare Hungarian weeds are associated with traditional extensive farming practices. They are particularly characterized by short, midsummer flowering periods and by preference for low nitrogen levels, but a range of trait syndromes must be considered to understand their ecology and conservation. Analyses based on trait‐divergence patterns, rather than trait‐convergence patterns, provide better insights into the functional composition of weed communities, emphasizing the importance of disruptive filters in weed community assembly and the need for improved methods to detect such effects.